package com.treasure.common.utils;

import java.util.HashSet;
import java.util.Set;

/**
 * snowflake 算法实现生成id
 */
public class SnowFlakeId {

    /**
     * 起始的时间戳
     */
    private final static long START_STAMP = 1480166465631L;

    /**
     * 默认数据中心
     */
    private final static long DEFAULT_DATA_CENTER_ID= 31;
    /**
     * 默认机器id
     */
    private final static long DEFAULT_MACHINE_ID= 31;
    /**
     * 每一部分占用的位数
     */
    //序列号占用的位数
    private final static long SEQUENCE_BIT = 12;
    //机器标识占用的位数
    private final static long MACHINE_BIT = 5;
    //数据中心占用的位数
    private final static long DATA_CENTER_BIT = 5;

    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATA_CENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATA_CENTER_LEFT + DATA_CENTER_BIT;

    //数据中心
    private static long dataCenterId= DEFAULT_DATA_CENTER_ID;
    //机器标识
    private static long machineId= DEFAULT_MACHINE_ID;
    //序列号
    private static long sequence = 0L;
    //上一次时间戳
    private static long lastStamp = -1L;

//    public SnowFlakeId(long dataCenterId, long machineId) {
//        if (dataCenterId > MAX_DATA_CENTER_NUM || dataCenterId < 0) {
//            throw new IllegalArgumentException("dataCenterId can't be greater than MAX_DATA_CENTER_NUM or less than 0");
//        }
//        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
//            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
//        }
//        this.dataCenterId = dataCenterId;
//        this.machineId = machineId;
//    }
    private SnowFlakeId() {
        this.dataCenterId = DEFAULT_DATA_CENTER_ID;
        this.machineId = DEFAULT_MACHINE_ID;
    }
    /**
     * 产生下一个ID
     *
     * @return
     */
    public synchronized static String nextId() {
        long currStmp = getNewStamp();
        if (currStmp < lastStamp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastStamp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStamp = currStmp;

        long value = (currStmp - START_STAMP) << TIMESTAMP_LEFT //时间戳部分
                | dataCenterId << DATA_CENTER_LEFT       //数据中心部分
                | machineId << MACHINE_LEFT             //机器标识部分
                | sequence;                             //序列号部分
        return String.valueOf(value);
    }

    private static long getNextMill() {
        long mill = getNewStamp();
        while (mill <= lastStamp) {
            mill = getNewStamp();
        }
        return mill;
    }

    private static long getNewStamp() {
        return System.currentTimeMillis();
    }

    public static void main(String[] args) {
        Set<String> idSet = new HashSet<>();
        SnowFlakeId snowFlakeId = new SnowFlakeId();
        for (int i = 0; i < 10; i++) {
            idSet.add(snowFlakeId.nextId());
        }

        System.out.println(idSet);
        System.out.println(idSet.size());
    }
}